The present invention relates to a zero-phase sequence protective device for protecting from burning the armature winding and the core of the rotor of a three-phase synchronous machine when a line-to-ground fault occurs within the synchronous machine.
According to the prior art protective method for interior faults of three-phase synchronous machines, interrupters are used to isolate the machine with a fault from the system, and concurrently the excitation thereof is interrupted. However this method has a defect that a finite time is required before the machine with a fault or short-circuit is isolated from the system so that the fault current in greater magnitude flows to the fault, resulting in the burning of the fault point. Furthermore, the prior art method has also another serious effect that in case of the occurence of a fault, a large second positive-phase sequence current flows into the armature, resulting in eddy currents in the core of the rotor and consequently the overheating and burning thereof.